Determination of the concentration of solutes in bodily fluids is often used for monitoring of medical conditions and treatments, diagnostics, health assessment, early disease indication and the like. Typically, the determination of the concentration of solutes in a bodily fluid requires invasive procedures, such as the drawing of blood, for diagnostic measurements. However, the drawing of blood can be a painful experience for a patient and it provides a degree of risk to the health care provider, vis-à-vis infectious disease, when drawing and handling a patient's blood. Furthermore, subsequent diagnostic measurements can be time consuming and expensive to perform. Desirably, a non-invasive diagnostic apparatus and method would permit collection and analysis of information regarding the concentration of bodily fluid solutes.
Non-invasive procedures have been developed that use the eye, and in particular the retina, of a subject to monitor and measure specific analyte concentrations. Examples of such non-invasive procedures include: glucose sensing through aqueous humor; reflectance of retina to determine haemoglobin, glucose, oxygen; and raman to measure macular carotenoid levels. However, these presently known approaches have had a number of drawbacks. Typically, current techniques suffer from poor sensitivity to changes in biochemical indicators within the fluid (e.g., blood) or tissue. The result is reduced accuracy in indicator quantification and therefore reduced reliability in determining the state of the blood and the health of the subject. To date, these shortcomings have precluded the acquisition of meaningful and reliable optical signals from the retinal tissue and have prevented widespread adoption of such methods.
U.S. Pat. No. 6,565,210 describes an ocular characteristic measuring apparatus capable of measuring a light-intensity distribution characteristic of a target image formed on a fundus of an eye and of determining the ocular optical characteristic of the eye on the basis of the measured light-intensity distribution characteristic. The disclosed device apparently removes “substantially all” scatter-reflected light from the light reflected from the fundus.
U.S. Pat. No. 5,919,132 discloses a method and apparatus for conducting on-line and real-time spectroreflectometry oxygenation measurement in a patient's eye following illumination of the eye. The device comprises a first optical system to transmit the axial central portion of a light beam reflected from the fundus of the patient's eye to a detector for spectroreflectometry oxygenation measurements. Further, the device comprises a second optical system for transmitting the axial peripheral portion of the reflected light beam to a second detector for visualizing the fundus of the patient's eye and positioning the light beam on the fundus without positioning error.
There remains a need for a reliable and accurate non-invasive method and apparatus for obtaining optical measurements useful in monitoring the health of a subject and/or of a retina of a subject.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.